There have been many measuring tools developed for accurately determining the diameter of a cylinder bore. Tools of this type normally consist of an apparatus that functions by contacting diametrically opposite points within the bore.
One common example of a tool used for measuring interior distances is a caliper. A basic caliper will normally be used in combination with a micrometer to determine a bore's diameter. A user initially positions the caliper so that the tips of its jaws span the cylinder bore and contact opposite points within the bore. The caliper is then removed from the cylinder and a micrometer is used to accurately measure the distance between the tips of the caliper's jaws.
Another tool often used for measuring inside diameters is a dial caliper. This type of tool combines a caliper with a dial indicator. The dial indicator is connected to the caliper's jaws in a manner wherein movement of the jaws causes the indicator's pointer to move. This tool enables a user to accurately determine an interior distance without the need for two separate tools.
A third device commonly used for measuring inner diameters is a tubular inside micrometer. The measuring device is fully received within the bore and a direct measurement is provided through a telescoping action of the apparatus. To increase the tool's range, extensions of known length may be added to the basic tool.
While being satisfactory for many uses, prior art measuring devices suffer certain failings. When taking a measurement deep within a bore, the prior art devices are often found to be either incapable of taking such a measurement or are extremely awkward to use. For a caliper-like device, the body of the tool must remain exterior to the cylinder bore at all times. Devices such as the tubular micrometer often cannot be placed or maintained in a proper position relative to the cylinder axis to enable accurate measurement. These difficulties are often magnified when a number of different readings are required to determine if the cylinder has become tapered, damaged or unevenly worn in some other manner.
The prior art devices are also difficult to use by a novice and require a significant training period. Even when an accomplished professional uses one of the prior art devices,, repeated measurements may yield different readings.
Another problem with the prior art devices is that one must guess where to properly place the tool to enable an accurate measurement of the bore's diameter. This can be a laborious process and sometimes results in the user measuring a chord of the bore in lieu of its true diameter.